Magnetic compositions containing iron, rhodium, and at least one member of the lanthanide series



United States Patent MAGNETIC COMPOSITIONS CONTAINING IRON, RHODIUM, ANDAT LEAST ONE MEMBER OF THE LANTHANIDE SERIES Paul H. L. Walter,Wilmington, Del., assignor to E. I. do Pont de Nemours and Company,Wilmington, Del., a corporation of Delaware No Drawing. Filed May 3,1962, Ser. No. 192,060

4 Claims. (Cl. 75-122) This invention relates to, and has as itsprincipal ob-' ject provision of, new magnetic materials useful for theinterconversion and control of various forms of energy.

Magnetic materials, inclusive of both ferroand ferrimagnetic materials,are broadly old and many such compositions are known. Similarly, manyenergy transducer devices based thereon are also known. However, thepreviously known ferromagnetic compositions suffered variously from oneor more inferior properties, qualities, or behavior. For instance, manyof the ferromagnetic compositions did not exhibit as high saturationmagnetization values as was desired for many outlets, nor did theyexhibit sufiicient corrosion, oxidation, or high temperature resistance.While some of these ferro-, ferrimagnetic compositions did exhibit therather peculiar property of an abrupt and large-scale increase insaturation magnetization with increasing temperature, those previouslyknown either exhibited this so-called exchange inversion temperature atrelatively low temperature and/or suffered from having too low a Curietemperature for successful application in many desired embodiments.

The iron/rhodium binary alloys of, for instance, Fallot, RevueScientifique, 77, 498 (1939), and Kouvel et al., General ElectricResearch Report No. 6l-RL- 2870M, November 1961, also exhibited thisabrupt increase in saturation magnetization with increasing temperaturewith a o of about 112 gauss cm. /g., i.e., 112 emu/g, as measured in a5,000 oersteds (or con ventionally a koe.) magnetic field, but at atemperature of only 350 K. (i.e., about 77 C.). Furthermore, thetemperature at which the material suddenly changes fromantiferromagnetic to ferromagnetic could not be widely varied withoutincreasing greatly the ratio of residual magnetization to maximummagnetization.

Recently there was discovered new and improved magnetic materials asdisclosed and claimed in the copending coassigned applications ofWalter, Ser. No. 177,230, filed March 5, 1962, and Ser. No. 177,229,filed March 5, 1962, based on metal alloys consisting essentially ofiron and rhodium in major proportions and in minor proportion,respectively, at least one other member of the first long transitionperiod of the Periodic Table of the elements of atomic numbers 21-30,inclusive, but exclusive of iron, and in the second application, againin minor amount, at least one other member of the second and third longtransition periods of the Periodic Table of the elements of atomicnumbers 39-48 and 57-80, inclusive, but exclusive of rhodium. These newferromagnetic materials exhibit good saturation magnetization values andhigh Curie temperatures and at the same time are outstanding incorrosion and oxidation resistance, and thermal degradation.

There has now been discovered a new class of ferromagnetic materialswhich not only exhibit very good saturation magnetization values andhigh Curie temperatures but also exhibit higher saturation magnetizationvalues at higher temperatures than the just referred to ferromagneticmaterials of the said copending coassigned Walter applications. Thesecompositions are also outstanding in corrosion and oxidation resistanceand thermal degradation, properties in which many or most v 3,144,325Patented Aug. 11, 1964 of the presently known magnetic compositions arefound wanting. They also exhibit very high hardness.

These superior magnetic compositions consist essentially of iron andrhodium in major proportion and at least one member of the lanthanum orlanthanide series of the Periodic Table of the elements of atomicnumbers 58-71, inclusive, viz., cerium, praseodymium, neo dymium,promethium, Samarium, europium, gadolinium, terbium, dysprosium,holmium, erbium, thulium, ytterbium, and lutetium. The iron and rhodiumwill normally be present in substantially equal atomic proportions butnot necessarily equal, since either may exceed the other by 20 atomicpercent. It is, however, always necessary that both iron and rhodium bepresent. The at least one rare earth metal of the lanthanide seriesrunning from atomic number 58-71, inclusive, which also must always bepresent, will range in amount from 0.01 to 0.20 atom proportion. Thus,the new superior magnetic compositions of the present invention arealloys of the formula wherein M represents a rare earth metal of thelanthanide series of atomic number from 58-71, inclusive; x is aninteger from -1 to 14, and generally 1 to 3; a and b, which can be alikeor different, are numbers ranging from 0.8-1.2; and c is a numberranging from 0.01- 0.20 and in the instance when x52, the requisite cscan be alike or different but still must fall in the indicated range.The subscript numbers a, b, and 0 refer to the atom proportions of therespective elements in the products. M can be different within the samedefined group when x is greater than 1.

A particularly preferred subclass of these new magnetic materialsexhibits a maximum saturation magnetization within a restrictedtemperature range and a very much smaller saturation magnetization attemperatures above and, below this range. These preferred mag neticcompositions exhibit a relatively low saturation magnetization at lowtemperatures which abruptly increases with increasing temperature, at aspecific temperature range for each composition, to a maximum saturationmagnetization many orders of magnitude greater than that exhibited attemperatures below this critical temperature range. This maximumsaturation magnetization slowly decreases with increasing temperatureuntil the Curie temperature is reached. On being cooled from the Curietemperature these preferred compositions exhibit slowly increasingmagnetization with decreasing temperature until a maximum saturationmagnetization value is reached and then abruptly exhibit a largedecrease in saturation magnetization, reaching ultimately a lowremanence saturation magnetization. The maximum saturation magnetizationis generally the same on decreasing temperature as that achieved onincreasing temperature. However, the temperature at which the maximumvalue is exhibited is somewhat lower on a decreasing temperature cyclethan an increasing temperature cycle, i.e., there is magnetizationhysteresis as a function of cycling temperature.

Not only is this subclass of the magnetic compositions of this inventionpreferred, but also devices for the interconversion and control ofvarious forms of energy based on this preferred class of magneticcompositions comprise another preferredportion of the present invention.Another preferred embodiment of the invention is directed to methods forpreparing these preferred magnetic products exhibiting these novelmagnetic properties, and also to the preparation of energy transducersbroadly based on such products.

The proportions of metals within the alloys of this invention can beexpressed in somewhat different terminology as follows: iron, about33.33-59.70 atom percent;

'phere.

50-150 amps.

- 7 a s rhodium, about 33.33-59.70 atom percent; and at least onelanthanide of atomic number 58-71, about 20.0- 0.415 atom percent. It isto be distinctly understood that at least one lanthanide of atomicnumber 58-71 is 4 a is used to indicate the residual saturationmagnetization of the sample in emu/g. The symbol a is used to indicatethe maximum saturation magnetization of the material in emu/g, and thecolumn headed temp-oindicates the temperature at which this maximumsatu- Compnsed Wlthm the deslgnated 20041415 atom per rationmagnetization value is attained. In all instances Ce and p to 14 Ofsllch elements can be P in all columns involving temperature the unitsare in C.

Th f ll g examples In Whlch the Parts are The saturation magnetizationdata were obtained using a by Weight are Submitted t0 illustrate thePresent lnvenmagnetic field of 15.75-16.00 koe. (i.e., kiloersteds ortion further and not to limit it. 15,75 0-16,000 oersteds).

Table I Anneal Heat 0001- Temp.- Composition Time, 111g T. ing Ts To a.Umnx mm! hours Fe/Rh/0.0833 Gd 40 132. 0 -195 Fe/Rh/0.0833 Tm 40 37 0 5110.0 138 Fe/Rh/0.0833 H'o. 40 127. 3 -195 .s Fe/1.2 Eli/.10 Er 2s 96 38 45. s 127 1.2 Fe/.8 Rh/.20 sm 2s 118. 4 -195 FG/Rh/.05 Tb/. 5 Nd 28127.4 195 EXAMPLE I An intimate mixture of 2.9833 parts of iron and5.4986 parts of rhodium, all in finely divided form was placed in a dieand pressed into a pellet. The pellet was then placed in thewater-cooled copper cup of a DC electric arc furnace. On top of thepellet was placed 0.6234 part of cerium metal in the form of a lump. Thefurnace was then sealed, flushed several times with purified argon, andfinally filled with argon at a pressure of one atmos- An arc was struckand the metals fused together. In operating this are, the copper was thepositive electrode and thoriated tungsten was used as the negativeelectrode, and the voltage was 5-25 volts and the amperage was Thecurrent was shut off and the sample turned over. The arc was thenrestruck and the sample remelted. This turning and remelting process wasrepeated to a total of eight times to insure homogeneity. Following thefinal melting, the furnace was allowed to cool and the product wasremoved. The metallic prod- ,uct was slightly magnetic at roomtemperature.

To further homogenize the sample and to encourage ordering of thecrystal lattice, the metal slug was sealed in an evacuated silica tubeand heated to 950 C. for 40 hours, after which it was cooled slowly toroom temperature over a period of 24 hours. After this annealingtreatment, the slug appeared superficially unchanged. However, it wasnow almost non-magnetic at room temperature, exhibiting a residualmagnetization of less than 2.0 emu/ g. On heating to above 118 C. themagnetization increased rapidly to a maximum of 106.5 emu/g. at 159? C.On further heating the magnetization fell off to the Curie point of 445C.

For brevity, the additional detailed examples illustrative of thepresent invention are covered in the following table in which these newmagnetic compositions were prepared as described in full detail inExample I in the foregoing with the indicated, variations in chargecomposition, annealing time, and the resultant different magneticproperties. As in Example I, in all instances the charge was arc-melted,turned, and remelted a total of eight times. In this table the chargedcompositions are in the indicated atomic proportions. The annealing timewas, in all instances, at 950 C., and the symbol T refers to thetemperature at which the indicated new magnetic composition undergoesthe rapid and large-scale change in saturation magnetization. The columnT (heating) lists the temperatures at which such a phenomenon occurs asthe sample is raised from a lower temperature, and the column headed T(cooling) indicates the temperature at which the sample undergoes theabrupt large-scale decrease in saturation magnetization on cooling froma higher temperature. The symbol T is used to represent the Curietemperature. The symbol Suitable specific compositionswithin the scopeof the present invention, i.e., those materials consisting. essentiallyof Fe, Rh, and at least one element of the lanthanide series of atomicnumber 58 through and inclusive of 71, include m ro oa 0.95 1.08 0-05! um dz, ds rr oai on rz an 0.9 1.0 0.01: 0.9 1.0 0.1 La on onsi 1.o 1.1Yo.os, ro os oae 1.0 l.2 0.15: m rz aoa Lo Lu m Lo m ons,

and the like. As stated in the foregoing, the present invention is notlimited. compositionwise to three-component compositions similar tothose just specifically named wherein there is present in the alloys Feand Rh in major amount and a minor amount of a lanthanide but is alsoinclusive of those alloy compositions consisting essentially of Fe andRh in major amount and relatively minor amounts of more than onelanthanide. Thus, the present invention is also specifically inclusiveof four, five, ,six, seven, eight, etc., element-containing alloyswherein the Fe and Rh are always present and in major amount, and theother elements are present in minor amount and are all lanthanides.Thus, to be specific, the presentinvention also includes the followingmulticomponent magnetic alloys:

and the like. While varying modifying'amounts of the lanthanides can bepresent in these new alloys which have Fe and Rh in major amount and twoor more of the said lanthanides, generally speaking there will be atotal of no more than 0.2 to 0.4 atom proportions of said othermodifying transition elements in any one alloy.

The novel compositions of the present invention exhibit a maximumsaturation magnetization at temperatures in the range 269 C. to +375 C.and Curie temperatures in the range +350 to +600 C. The preferredmagnetic compositions also exhibit increasing saturation magnetizationwith increasing temperature in a tempera-.

magnetizations in the higher temperature ranges. Those exhibitingmaximum saturation magnetization at very low temperatures are especiallyuseful in devices such as refrigerators and temperature-sensitivecontrols operating at temperatures near the boiling point of liquidhelium and below. The manner in which saturation magnetization varieswith temperatures can be controlled by modifying the composition of theferromagnetic products. The most outstanding compositions exhibit a verylow residual magnetism below the lower ferromagnetic transitiontemperature.

These novel magnetic compositions are prepared by heating mixtures ofthe elements or compounds of the elements to a temperature in the rangefrom 600 to 2500 C., or higher, as equipment and vapor pressurelimitations dictate within the normal practice. Temperatures of 700 to850 C. and from 1200 to 1700" C. are usually employed. Temperatures ofat least about l550-1600 C. are generally necessary if the compositionsare to be melted, which is preferred, preferably in an arc. The time ofheating is not critical but should be sufficient to permit completereaction of the ingredients. Heating times ranging up to about 50 hoursfor the lower temperature ranges are necessary to effect appreciablesolid state reaction. Longer times can be useful in some cases,particularly, for instance, if it is desired to prepare the compositionin single crystal form. Generally speaking, the most eflicient techniquein the sense of obtaining the most complete reaction is to carry out thereaction in the melt for time periods of from at least 5 to about 60minutes or longer. Most preferably the reaction is carried out in themelt in an arc furnace with repeated remelting and repositioning toassure homogeneity.

Heating can be carried out at amospheric pressure with the reactantsprotected by a blanket of inert gas such as helium or argon.Alternatively, the reaction can be conducted in an evacuated vessel. Itis also possible to employ superatmospheric pressure. The reaction canalso be carried out in sealed vessels under the autogenous pressuredeveloped by the reaction mixture at the reaction temperatures. Sincethe preferred techniques involve effecting reaction in the melt, it isnormally preferred to carry out the reaction in inert refractorymaterials under reduced pressure or under a protective blanket of aninert gas.

The materials employed in preparing these new compositions can be theelements themselves or any of thebinary or ternary combinations thereofas called for by the desired stoichiometry. Thus, to prepare Fe/Rh/Cethe three elements themselves can be charged or the necessary Fe/Rhbinary can be separately prepared previously and then mixed with therequisite amount of Ce and reaction eifected to form the desired ternarycomposition. In any event, it is preferred that the materials be inpowder or granular form and that they be well mixed before heating iscommenced.

' The starting materials are employed in such relative amounts that theresulting mixture contains the desired proportions of Fe/Rh and therequisite at least one lanthanidel Thus, to prepare an Fe /Rh /Lu therespective elements or binaries are charged in the indicated relativeatomic proportions.

After the desired preparative heating cycle has been completed, thereaction mixture is cooled and, if desired,

subjected to purification, e.g., by extraction with acids or,

component.

parative heating 0nd cooling cycle, whether or not any interveningmechanical, chemical, or magnetic purification is effected, be heated toan elevated temperature in the range 800-1000 C. or higher and held atthis temperature for relatively long periods of time, e.g., from 24 tohours or so, in an inert atmosphere, i.e., under evacuated conditions orwith a protective blanket of an inert gas such as argon or helium. Then,the compositions of the present invention are further annealed carefullyby final slow cooling from this temperature to room temperature over aperiod of approximately 24 hours.

The novel magnetic compositions of this invention exhibit severalmagnetic characteristics which make them especially valuable for use invarious specific applications. The novel lower ferromagnetic transitiontemperature is a distinguishing feature conferring unusual utility onthese materials. Particularly outstanding are the relatively highsaturation magnetization values exhibited by these compositions, as wellas the high Curie temperature and good values of saturationmagnetization exhibited at the maximum with increasing temperature belowthe Curie temperature. All the compositions are resistant to corrosion,oxidation, and exhibit good magnetic behavior at elevated temperatures.

The preferred products are useful in devices for the interconversion andcontrol of various forms of energy such as solar motors,temperature-sensitive inductors, thermally activated clutches, andtemperature compensators in devices based on conventional magneticmaterial where sagging of magnetic properties with increasingtemperature is functionally deleterious. In their essential features allof these devices comprise at least three components, viz., the magneticcomponent described previously, suitable means for applying a form ofenergy to and from the magnetic component, and suitable means forutilizing the output from the magnetic For some applications, thedevices of the present invention can include means for controllablymagnetizing and demagnetizing the magnetic component.

At temperatures within the ferromagnetic range, these compositions canbe used in any of the conventional applications for ferromagneticmaterials for which their properties render them suitable, e.g.,electromagnets,

high-frequency coil cores, information and memory storage elements, andthe like.

In the preferred devices the elements which provideheat to or removeheat from the magnetic element, which magnetize and demagnetize themagnetic element, and which collect and detect the new form of energyproduced are conventional in the art. For example, by introducing apivotal element, with a magnetic component as just described, in amagnetic field and having means for magnetizing the magnetic component,the pivotal elment can be caused to move in said field. In this way,mechanical work can be done. The pivotal element can be an armature, anoscillating arm, or a metering device.

The preferred compositions of the present invention are useful as theactive component in forming temperature responsive electrical inductorscomprising, usually in combination, a metallic core consisting at leastin part of one of the present magnetic compositions with or without asecond material exhibiting a magnetic permeability which issubstantially invariant with temperature, and an electrical conductorwrapped around said core. These temperature responsive electrical(magnetic) inductors are widely useful in any circuits in whichinductance is a significant parameter. Thus, these inductors based onthe present magnetic compositions can be employed as an element of thefrequency-determining circuit of a sine-wave oscillator or ashigh-temperature safety device to reduce circuit current With increasingtemperature or as a current-controlling device in which the controlcurrent flows through a heater wind- 7 ing on the temperature-sensitiveinductor. In addition, these temperature-responsive inductors can beused in conjunction with a Wide variety of conventional core materials,including both the metallic and oxide types, representative of whichlatter are, for example, the ferrites.

In view of the increasing saturation magnetization with increasingtemperature below the Curie temperature, the preferred materials of thepresent invention are useful in forming temperature responsivemagnetically operated rotary forcecouplings comprisingin combination, apai'rof relatively rotatable elements to be coupled disposed adajcent toone another in a common magnetic flux path, a permanent magnet, and oneof the new magnetic compositions of the present invention which exhibitsa changing permeability accompanying a reversible first order transitionfrom a'first solid state phase to a second solid state phase at a giventemperature, both disposedin said common magnetic flux path, thepermanent magnet and the magnetic composition of the 'presentinventioncompleting a magnetic flux circuit between the said elements ofthe pair coupling one of the elements with the other in that'temperaturerange when the magentic composition of the present invention exists in afirst solid state phase and uncoupling the elements of the pair as thetemperature decreases when the substancegexists in a second solid statephase, and obviously the reverse and in cycles.

The, preferred compositions of the present invention are alsouseful inthermomagnetic devices as the work'- ing substance therein, said devicesbeing useful for effecting heat transfer, i.e., serving as heat pumps,e.g., a refrigerator. These new magnetic compositions insuch devices inview of the first order solid phase to solid phase transition withchanging temperature with accompanying relatively large change ininternal energy content in going through the transitionwill function asthe said working substance in said devices with allied coupled magneticmeans for cyclically inducing Salid transition in a direction such as tolower the temperature of the substance when one solid state phase isattained and to increase the temperature when the'other solid'statephase is attained, along with an allied heat source and a thermal sinkrelative to one of the solid state phases individually adapted to effectheat transfer sequentially with respect to said substance.

With respect to the thermomagnetic working capability of the preferredcompositions, they are of particular interest in the formation ofgradient objects comprising the said'ma gnetic materials varying incomposition angularly about a point or axis or varied along one or moreselected lines, which need not be straight, in the said elements inthermal switches, and the like, and are particularly outstanding becauseof the possible ready and precise adjustment of device operationachievable to suit particular environmental conditions obtained with thegreat control possible through the narrow compositional changes Thesepreferred materials are also useful as the working substance in a methodof information storage and retrieval wherein a recording membercontaining one of the new magnetic compositions of this inventionsubstantially homogeneously distributedtherethrough is exposed to aread-in beam, modulated patternwise in accordance with information to bestored from a temperature variation inducing component, therebyestablishing in the said recording member regions of relatively higherand relatively lower intrinsic magnetization corresponding to saidinformation, maintaining said elementafter said read-in at a temperaturewithin the thermal hysteresis range, and reading out the storedinformation by exposing the element at said temperature to a lowintensity electron beam whereby deviations in said beam corresponding'tothe stored information are produced and converted into electricalsignals. Intrinsic magnetization is used here as defined by Cusack, TheElectrical and Magnetic Proper ties of Solids, Longmans-Green & Company,London, 1958, page 315.

The first order solid phase to solid phase transition accompanied bythermal hysteresis which is exhibited by the preferred materials ischaracterized by abrupt change not only in the magnetic properties butalso in a number of the other physical properties of the materials andany of these properties can be employed in any sensing or read-outmethod. Thus, after modulated read-in, readout can be based on thechange in electrical resistance of the new magnetic materials serving asthe working substance of said recording member simply by providingread-out means sensitive to changes in resistance. Alternatively,read-out can be based upon changes in a linear dimension or in a volumeof the working substance as desired.

Because of their outstanding magnetic properties coupled with goodstability to temperature, atmosphere, corrosion, oxidation, and thelike, and particularly because of the relatively high Curie temperaturesthat they possess, the preferred magnetic materials are broadlyoutstanding as the working substances in various devices whereby,generically, magnetic energy is changed controllably to mechanical,electrical, or thermal energies; mechanical energy is convertedcontrollably into electrical, magnetical, or thermal energies; orthermal energy is controllably converted to mechanical magnetic, orelectrical energies.

More specifically, the preferred compositions of. the present inventioncan serve as the working substances in magnetic switches,radiation-intensity meters, reciprocating engines, devices formaintaining constant temperature difference between two zones, magneticbalances, thermomagnetic generators, solar motors, temperatureindicators, image-forming components, magnetic flashers, variableresistors, differential transformers, temperature responsive resonators,and the like.

Since obvious modifications and equivalents in the invention will beevident to those skilled in the chemical arts, I propose to be boundsolely by the appended claims.

The embodiments of the invention in which an exclu sive property orprivilege is claimed are defined as follows:

1. An alloy composed of (A) iron, (B) rhodium, and (C) at least onelanthanide of atomic number 58-71 in the atom proportions of 0.8-1.2 of(A), 0.8-1.2 of (B) and 0.01-0.40 of (C).

2. An alloy of claim 1 in which (C) is cerium.

3. An alloy of claim 1 in which (C) is gadolinium.

4. An alloy of claim 1 in which (C) is holmium.

N0 references cited.

1. AN ALLOY COMPOSED OF (A) IRON, (B) RHODIUM, AND (C) AT LEAST ONELANTHANIDE OF ATOMIC NUMBER 58-71 IN THE ATOM PROPORTIONS OF 0.8-1.2 OF(A), 0.8-1.2 OF (B) AND 0.01-0.40 OF (C).